text:
EASA procedures for radio/comm failure under VFR rules
Trying to find the VFR communication failure procedure in EASA, but can't find anything clear enough, maybe someone have a link for clear instructions for that procedure?
I want to figure out what should I do in case of comm failure under VFR rules when -

I am in uncontrolled airspace? (G or vfr in E - controlled but communication not required) can I continue my flight? As I am not required to have two way communication (at least in the Czech Republic) and just somehow deal with the destination airport? Or should I land ASAP ?

What should I do if I am crossing controlled airspace? Continue with my clearance? Or leave the controlled airspace asap?

In case of flight into a controlled airport and communication failure just before the traffic Circuit, what to do? Continue to the circuit and hope someone will understand that I am without a radio and use lights?

I checked all the VFR manuals I found but didn't find any clear instructions, just "squak 7600 and land in the nearest suitable airfield" but it feel too simplified for me...

Closely related: https://aviation.stackexchange.com/questions/3794/how-would-an-airplane-land-if-the-on-board-radio-breaks-down

@Jamiec, thanks! but from what I see in the answer it's related to the FAA, I believe that there should be some differences between the FAA procedures and the EASA ones, am I wrong ?

I don't think they're materially different. I wrote that answer with reference to an FAA publications but I fly in the UK and would follow much the same procedures (even though we're no longer EASA!)

Much of that answer was also written with reference to https://www.cfinotebook.net/notebook/flight-hazards-and-safety/lost-communication

Surely it matters what sort of controlled airspace you are in?  Certainly it does in the US, there's a lot of controlled airspace (namely Class E) that you can fly in VFR without talking to anyone.  Question strikes me as being overly broad-- but maybe it wouldn't to someone more familiar with EASA-- ??

Actually to put a finer point on it-- Class E airspace is controlled airspace in the US, and that's surely true for EASA too.  Please edit the question.  (Pertains to content after first "bullet" point.)  Way too many people think the definition of "controlled airspace" is "I have to talk to a controller to go there."  That's wrong.  In the US, controlled airspace is anything other than Class G, and I suspect it's the same in EASA-land too.

@quietflyer, my understanding is that outside of the USA Class E is relatively rare—at least low-level.


text:
What are the spikes on Ingenuity's blades?
I am puzzled by the spikes on Ingenuity's blades (marked by a red box in the image below).

What is their function ?
Are these special to Ingenuity?
Why don't they collide during high RPM?
Don't they induce unwanted drag and/or turbulence?

I have tried searching NASA's website but couldn't get a description of these particular featuers. Answer to any part is appreciated.

Might be better on the Space SE: https://space.stackexchange.com/questions ?

@simonatrcl thnx didn't know about it .. should I delete here?

If you open it there, then delete it here (1 Q open on two Stacks is considered bad form). Or you could ask a moderator to move it to space - but I'm not sure how to do that. Good luck anyway!

While definitely also on topic at Space.SE, I think this question is on topic here. It is about a helicopter after all (even if it doesn't fly on this planet). So IMHO you can leave the question here.

@simonatrcl 1 Q on two Stacks may be considered bad form, but it is fully legit since the question is on the boundary between two worlds.
I think Stacks'users should focus much less on form. or, if they really have to, to focus on the form they give away knowledge or nothing, aparts from some crappy rewards such as "points".
Read:
https://meta.stackexchange.com/questions/104947/is-stack-exchange-a-for-profit-company-if-so-how and try to check the history of similar sites (i.e. Couchsurfing, just to mention a very close concept of build large community for free, then get the paycheck)

@EarlGrey - Thanks, and good to know. I'm just going on what I've seen happen.

@EarlGrey well you are wrong about dup questions, and obfuscating with a bunch of politics doesn't make your case. It's not weird for a community to have rules.

@Harper-ReinstateMonica "a bunch of politics" from someone claiming from his username to be interested in common goods. Funny!

@simonatrcl The better way is to hit "flag..." and "other..." and say "mod please move to .se".  An author request would certainly be granted, any other would be considered.

In the Mars Helicopter Technology Demonstrator paper these are refered as "Chinese weights" and the purpose stated is

Chinese weights provide a restoring force on the blade moments when
under centrifugal loads thereby reducing the torque requirements on
the swashplate actuators.

Searching for the term leads mostly to RC sites, for example this explanation.
Being placed close to axis of rotation (and presumably heavy but small in volume) the aerodynamic effect should be minimal compared to the rest of blade.
My assumption is that this can be quite specific to Ingenuity (and RC models) because limited torque available in electrical actuator servos compared to control system of full-scale helicopter. (But it is my guess only.)
Edit: I have borrowed an image from https://mars.nasa.gov/resources/25043/mars-ingenuity-helicopter-3d-model/ (go there and rotate the model yourself to get a better idea how counterweights are placed) and tried to sketch how the force balance looks like:
Red arrows are centrifugal forces exerted on counterweight or blade's center of mass respectively. These forces are always perpendicular to the mast (rotational axis). Then, each of them can be broken into two orthogonal components -- parallel with blade pitch axis (green) and perpendicular to it (blue). Note that one blue arrow lays above pitch axis and second under, so they produce opposing torque and can cancel each other.

I thought they were blade counterweights at first, as is used on constant speed counterweight propellers since forever, but if they were blade counterweights, the ones for the upper rotor would be on top same as the lower one, since they are to provide a coarse pitch moment and presumably both rotors are lifting in the same direction while spinning in opposite directions.  It doesn't make sense that the upper rotor would have counterweights that tend to make the blades go flat.  Also, if they were counterweights, it's inefficient to have most of the meat at the base.

@JohnK if I understand it correctly then both pitching moment to be compensated and added moment through the counterweights is purely due to inertial forces (not aerodynamic and neither gravity), so it should not make (much) difference if they are upside down or not. "At the base" .. you mean of the blade? I guess it is some design compromise in play here. It is not only radial distance (which adds centrifugal force) but also off-the-blade-axis position (which creates actual pitching moment) which is important for force balance and not least aerodynamic consequences.

Actually in the linked paper the diagram shows both counterweights downwards, but prototype photos have them both upwards.

If they're being used for that purpose, the counterweights will be tuned to produce a pitching moment (from wanting to trail the blade) that is more or less the same as the blade aerodynamic pitching moment, and if is just right they will cancel each other out and the blade with have no pitching moment in some operating range so the servos have little resistance to work against.  There my be large weights at the tips of those little fins that are not visible in the pics, but normally you would expect to see some kind of mass at the top of each one.  In the video they are like the OP pic.

Yes, I'd expect weight located in the tip. Better view of the whole assembly: https://mars.nasa.gov/resources/25043/mars-ingenuity-helicopter-3d-model/ -- in the model there are counterweights about the right position to balance mass of each blade -- if you imagine cetrifugall force on counterweight and large area of each blade and its component perpendicular to pitch axis, these will cancel each other regardless which direction specific counterweight points. For aerodynamic forces, I guess you can get away with aligning pitch axis so that it intersects center of pressure.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
Performance metrics of a propulsion system - optimising a propulsive fan system
I'm designing an electric fan propulsion system for a hybrid-electric business jet. The hybrid business jet uses a series hybrid configuration and distributed electric propulsion. The electric fan propulsion system is for the distributed electric propulsion part of the engine and consists of the fan, intake duct and propulsive nozzle. So far, I've designed it so that the efficiencies of each component is as close to 1 and optimising the fan pressure ratio so the mass flow rate is large and the exit velocity is small (to improve propulsive efficiency). I'm currently unsure whether there are any other parameters I'm failing to consider and would like some more insight.

As has been pointed out fairly recently in another comment elsewhere (can't remember where), this sort of question should not be viewed as being about resource allocation.

My comment was meant to be in support of your question as a legitimate question. If you find the help pages for the site, you'll find a note about questions about resource allocation being not allowed-- I interpret this to mean "where can I buy product x", or maybe "where can I find a book addressing topic y".  Most likely including "where can I find the data sheet on component z".  Anyway welcome to ASE.  I suspect most of the "close" votes may have related to a possible perception that the question was a broad engineering question possibly not really focussed on aviation.

@quietflyer  I agree but the OPs comment on the answer below makes it clear that resource location was the main motivation of the question. However since the edit it's much better.

Well, if all you care about is the fan performance by itself, then you've pretty much got it.  Maximize the component cycle efficiency and maximize the propulsive efficiency and that's it.  But if you want to start getting more real-world, then things to think about:

Off design conditions.  You can perfectly optimize efficiency at one condition (i.e. for a large commercial airliner this would be cruise: Mach 0.8 @ 40,000 ft), but the thing still has to have acceptable performance at other conditions (e.g. takeoff, Mach 0 @ 0 ft).  You may have to compromise on cruise efficiency to get acceptable takeoff performance.

Since this is an electric fan, it will be driven by some kind of a motor. That motor will have some speed where it is most efficient.  That may not be the speed at which your fan is most efficient.  You'll need to match the two of them to maximize overall aircraft efficiency.

If you want to go even one step further, that electric motor has to get power from somewhere. Presumably a battery.  To get peak efficiency from the motor might demand X current at Y voltage, but your battery might be optimized for less than X current.  Again, you may need to match the power source to the motor.

If you want to go even further, there are a number of real-world turbomachinery considerations to deal with including: Operability / stall margin, Inlet distortion tolerance (i.e. crosswind), Fan blade aeromechanics (i.e. flutter)

No I don't know of any books sorry

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Component of net fluid force (lift + drag) along a 2D wing's chord cannot cause a torque,
I've been struggling a bit to find a satisfying explanation for why the component of net fluid force along a 2D wing's chord cannot cause a torque.  At the moment (no pun intended), I'm only considering a symmetrical wing, not an airfoil.  Say, a rectangle.
I have two explanations:

The cross-product formula gives zero torque, since the component of net fluid force along the wing's chord is parallel to the moment arm, and so the sine of the angle between them is zero.

The component of net fluid force along the wing's chord cannot generate a torque; it can only translate the wing, with a push or a pull.

The component of net fluid force along the wing's chord cannot generate a torque because such a force is generated from fluid pressure around the wing that cancels out, and so only the perpendicular component of net fluid force is associated with a pressure imbalance around the wing, which can cause a torque, namely if the aerodynamic center is not at the center of mass.  I feel this is not quite right ...

The above explanations are unsatisfactory to me, for some reason.
What point am I missing that could help me feel more confident about the idea?  Preferably, something that's physically intuitive.
Should I instead not overthink it, and simply treat the cross-product formula as a definition of the torque force?

The airfoil has no curvature, so the pressure distribution, when the angle of attack is zero, on the upper and lower are the same. Bernoulli's equation for incompressible flow (or the compressible equivalent) gives an inverse relation between velocity and pressure. Since the air has to travel along the same length and shape on both sides, the velocity distribution is the same and therefore so is the pressure distribution. Pressure cancels on both sides and there is no aerodynamic force or torque. For this situation, the torque at the aerodynamic center (which never depends on the angle of attack, by definition) is zero.
When we increase the angle of attack, the pressure distributions are no longer the same (generating lift and drag), but the torque at the aerodynamic center has not changed (because it doesn't depend on the angle of attack).
The total torque on the wing is just the torque of the airfoils integrated along the wing. If we integrate the torque at the aerodynamic center along the wing, we get zero torque. And zero torque at one point means zero torque at all points, for a rigid body.

Hi Steve, I'm not confident in this answer, but your pressure-differential argument is one that I'm interested in.  I've put it into my own words and thoughts, in my edit to my question -- feel free to edit your answer or leave a comment.  Thanks so much.


text:
Is "medical" oxygen system suitable for part 91 aviation use?
I am, in a somewhat desultory fashion, considering obtaining an oxygen system (for use in the U.S. under part 91, perhaps sharing with some passengers).
An initial search suggests that one can buy a 15 cu-ft tank with the extras (regulator, tubing, cannulas) from an aviation supplier for around USD $700
I also see that I can get a medical system for about $125 (with just a single stretch of tube, basic regulator, (but no flow-meter) and cannula).
I know that medical oxygen is sometimes  disparaged for perhaps containing too much moisture, but I figure I could simply refill it with ABO anyway, right? I also read that moisture is unlikely to be present in reality today, and further that for the kind of cabin pressures I would be flying (unpressurized A/C and below 15,000' absolute maximum) this is unlikely to be an issue. But perhaps I miss something.
So... is there a compelling reason to spend the extra? Or is it likely that I have completely misread specs on things. Am I absurdly off the mark with the pricing for an aviation system (did I look at the wrong supplier, perhaps!)?

Welcome to aviation.SE! This question has some related information.

I saw that question when formulating mine, and I admit I'm really unclear as to the relevance of the whole part 23 discussion. Part 23 is aircraft certification, and this is not part of the aircraft. It's true that it does include a discussion of using portable oxygen to satisfy the requirements of part 23, and puts constraints on that. But I don't think that's relevant, as I'm not trying to satisfy part 23 using portable oxygen, I'm trying to satisfy part 91. And to be honest, I'm more interested in the pragmatic aspects of safety/usability. Though perhaps I should take a wider view.

Though to be fair, I missed the middle opinion on legality. Though that doesn't appear to offer much substantiation and doesn't directly address my dual topics of is it sensible, am I missing the pricing aspect.

It's generally well-understood that all the O2 comes from the same huge tank. While it might be labeled industrial-, medical-, or aviation-grade, if it comes from the same tank then it's the same stuff. That being said, if you are not using it to meet Part 91 requirements, i.e. time at altitude >= 12,500, I would think that it's as perfectly legal as breathing any other gas you care to.

Well, for myself as PIC, it would be for part 91 requirements, at least sometimes. And I would want the equipment to be "suitable" for my passengers comfort and health. I got altitude sickness one time from 90 minutes at 15,000' and I wouldn't wish that on anyone!

You are not certifying an aircraft so part 23 does not apply. Part 91 requires specific types of equipment only when flying above FL350 as follows:

91.211(b)(ii) At flight altitudes above flight level 350 unless one pilot at the controls of the airplane is wearing and using an oxygen mask that is secured and sealed and that either supplies oxygen at all times or automatically supplies oxygen whenever the cabin pressure altitude of the airplane exceeds 14,000 feet (MSL), except that the one pilot need not wear and use an oxygen mask while at or below flight level 410 if there are two pilots at the controls and each pilot has a quick-donning type of oxygen mask that can be placed on the face with one hand from the ready position within 5 seconds, supplying oxygen and properly secured and sealed.

In this one case a mask rather than a cannula is required and in one condition it must be a quick donning type.
At up to 15kft this does not apply, nor do passengers need to have oxygen by regulation. The label on the equipment is immaterial and all other references only state that when oxygen is required it shall be made "available", so your medical solution is ok with the FAA.
From a practical point of view some people get headaches as low as 10kft without oxygen, so having a provision to share might be useful although it sounds like you have been flying so far without. The "single stretch of tube and cannula" also needs a regulator and flowmeter. Oxygen is made by the way by the same companies for multiple purposes, so variation in moisture content is not an issue.
Aviation equipment costs more as the market is small. Like any product you can shop for better prices. The only step change in price that I would pay for is a pulse system, and only if I intended to use it a lot as they can cost $800 per user just for the pulsing device. These release oxygen only as you breathe in, and so conserve the amount consumed for a given saturation.

Good point on the flow-meter. What I was looking at has a $25 regulator, but no flow-meter. Anyway, I suspect you've likely hit the key points (and yes, visitors here from the low parts of the country sometimes get altitude sickness just from going for a modest hike.)


text:
Engine Bearings Damage in Radial Engines
Studying the P47's dive performance in DCS, I noticed how it's easy to damage the engine bearings if you windmill the prop at high speed.
Doing some research, I discovered that all radial engines are prone to this type of damage.

If,  because  of  insufficient  gas  load  (manifold  pressure),  the  propeller  is  allowed  to  drive the engine, the  resultant force on the crankshaft is applied  to  the opposite side of  the crankpin, where the oil supply is not optimised, and may quickly damage the bearing.    This damage  worsens  over time and  eventually  the bearing will  fail.  Failure  may occur several hours after  the  initiating event,  and therefore a  pilot may inadvertently damage the  bearing without seeing any immediate symptoms  requiring maintenance intervention.   The  engine is designed  to cope with some reverse loading  for brief periods,  for example  when  the propeller  is driven at  lower airspeed when landing, but  critical damage may occur quickly at higher speeds
Source: AAIB Bulletin: 10/2021 / G-INVN / AAIB-26839 (PDF)

I can't understand at 100%  why V, Inline , boxer ecc.. engines don't suffer of this problem too.
Probably the reason is due the load distribution that's completely different, but not sure.

Other source:
https://forums.eagle.ru/topic/260841-engine-bearings-and-how-you-can-keep-them-happy/

You are talking about the crankshaft thrust bearings, not the main journal bearings no?

I think that the damage is shared between both bearings; but probably the more damaged are the thrust bearing. I am going to share the links of where I found this information; one of those it's a report of a Sea Fury Crash. Let me know if you need more infos. Thanks for the help

If you read the second link carefully, it describes everything quite precisely, so I'm not sure why you're posting this question.The master rod is getting loaded on the opposite side of the oil feed hole when the prop is back driving, and the pressure on that side is insufficient to keep the metal apart under high backdriving loads,which are all concentrated on just two master rod bearings for all cylinders.Other engines don't suffer from this because those loads are distributed across individual connecting rods and the pressures trying to squeeze out the oil at the rod big end are much lower.

I agree with @John but I'm not convinced by the explanation in the article, as this reverse load also occurs when the engine is decelerated, not only when windmilling.

As I specified in the post, is clear that the loads are distributed in a completely different way in normals engine configurations; but there should be some damage related to windmilling also in them, but in a engine equipped with a constant speed propeller I never heard of that. (except going beyond engine RPM limit)

I think I understand the concept of that is going on.The master rod's bearing is being pushed on by the articulating rods in sequence, which tends to make them push on the same point on the crank pin, so if you clock the oil hole in the crank pin at spot X, that spot is always facing the articulating rod of the cylinder being fired as they go around, and therefore when back driving, the crank pin is now pushing on the master rod bearing at a point 180 deg away opposite the crank pin's oil hole.Normally the loads have declined where this doesn't matter, except in an extreme high speed windmill.

This all could be condensed into an answer, but oil deprivation seems to be key.  A straight crankshaft may have oil splashing equally on all sides, whereas the radial is famous for oil tending towards the bottom.  I'm also seeing all pistons turning one wheel on the radial.  With the inline, the heavy crankshaft can be absorbing differences in piston pressure better.

Thanks for all your replies! They were very helpful to understand completely the differences. The last comment of Robert completed the pieces that I was missing!! Thanks again! Airplanes are cool


text:
Why in the past were weather radars not used on fighter jets?
As far as I know, the weather radar is something that has been implemented very recently in fighters jets, from what I understand in modern radars it is possible to switch in various modes including the "weather" one.
Except for the technological reason, why in the past has it never been implemented?
Is it only due weight and space available? (And because the possibility of damage for an all-weather fighter jet is remote?)

Harrier that flew into a hail storm

What is the photograph and why did you include it?

@A.I.Breveleri It's an harrier that flew into an hail storm.

In which range of years are you interested?  If you were to change the question to “Why didn’t fighter jets made between  19?? and 19?? have onboard weather radar?”  What years would those be?

Great question! Yes, size and weight. Fighter aircraft need the kind of radar that allows them to detect and track targets. The majority of military fighter aircraft have attack and reconnaissance radars operating in the 8.5-11 GHz and 13-18 GHz bands with a large number operating in the upper portions of the 8.5-11 GHz band.
Weather radars are different animals which operate on one or more of three groups of frequencies depending on the environment they are analyzing.

S-band (2700–2900 MHz), in tropical and temperate climate areas, for
example, in areas where hurricanes, tornadoes, large hail and monsoon
or heavy rain are common.
C-band (mainly 5600-5650 MHz band), in climates where attenuation by
intervening heavy rain or large hail is a very minor issue.
X-band (9300-9500 MHz), in shorter-range hydrological and
meteorological applications such as urban and mountain valley
hydrology.

"Airborne weather radars, which require greater directivity, operate in 5.2-5.9 GHz and 8.5-11 GHz bands. The choice of these two bands for airborne weather radars indicates a dual trade-off of functional requirements: one is between storm penetration/scattering and the other is storm penetration/equipment size. If there is too much scattering, the radar will not penetrate deeply enough into the storm to see its full extent. However, if too little energy is scattered back to the radar, the storm will not be visible on the radar scope. The larger aircraft use 5.2-5.9 GHz band weather radars, even though they are larger and heavier, because of the better storm penetration capabilities and longer range performance. The majority of smaller aircraft employ lighter weight 8.5-11 GHz band weather radars that provide adequate performance."
Because of these differences, designers would have had to install two radar systems, or a much more complex multimode system. To fighter jets, attack and reconnaissance is much more important to the missions they undertake than analyzing weather.
Technology is constantly improving, though. Many aircraft these days have avionics packages that rely on ground data links to obtain accurate weather depictions. It makes much more sense to do that than to try to jam more hardware into already tightly packed avionics bays. There are better ways to use that weight and space, such as for fuel or ordnance.
Sources: Radars and the Electromagnetic Spectrum Introduction

and of course not wanting to give away your location by emitting in the EM spectrum during most combat operations (especially for ground attack aircraft). Which going undetected is one of the reasons you may prefer to fly those very missions in inclement weather.


text:
How to calculate DDM in a ILS dual frequency system?
I'm working in a project where I have to process ILS baseband signals. I have no problem obtaining DDM value from single frequency signals, nor the individual components of a dual frequency signal (DDM from clearance signal and DDM from course signal).
Now I need to merge those two individual DDM values (in dual frequency systems) to obtain an unified DDM value, similar to what Rohde equipment does (see figure below).

I've been told that I can obtain this
$\sum DDM$ value either:

As a function of individual DDM values: $\sum DDM = f(DDM_{clr}, DDM_{crs})$. But I'm not able to find the actual function $f(·)$.
Mixing clearance and course signals at baseband, so both components add up resulting in only one ILS-alike signal, and then calculate DDM from this new signal.

Are any of these methods valid? If not, how can I obtain $\sum DDM$ in a dual frequency system?

Hello Leroy, welcome to aviation.stackexchange.com! Your question is related to aviation (instrument landing system/ILS), but it is very much in the field of radio signal engineering (difference in depth of modulation/ DDM). It may take a while before someone comes along with an answer. Perhaps it is a better fit at another stackexchange site, although I am not entirely sure where (ham.stackexchange electronics.stackexchange or dsp.stackexchange ?)

I'm voting to leave open. It's related to this question which was answered by @mins. He may be able to answer with authority. My interpretation of Annex 10 is that the SUM DDM is the is difference between the sums of the two 90 Hz tones and the sum of the two 150 Hz tones, but I can't say it with confidence.

In the regions where the clearance signal dominates the course signal in power (receiver illuminated by one of the course sidelobes), the DDM is set to full scale deviation, no actual DDM is calculated, in the other region (receiver illuminated by the course main lobe) only the course signal is used to produce the DDM signal. When illuminated by a sidelobe, the receiver must still determine on which side of the main lobe this sidelobe is, to set the indicator on the correct extremity of the scale. The clearance DDM is used for this determination. I don't see why we would sum the two DDM.

Thank you for the warm welcome. I may have stated the question from a slightier DSP perspective, but the core question is how that SUM DDM value is computed, which is more specific to aviation than DSP (I'm pretty sure DSP community would send this question back to this StackExchange). Then I can figure out the signal processing myself.
@Gerry, could you reference me to which paragraph from Annex 10 you are talking about? Is it paragraph 2.7.x?.

@mins, if I understood correctly you are saying to lock to receiver to the signal with higher power and basically ignore the other, right? I understand the logic behind it, and it's coherent with paragraph 2.7.1 from Annex 10. But our client asked for that SUM DDM, as done by Rohde (see figure from question), and I can't figure out how this value is obtained (they don't seem to be locking the receiver to the high power component either). Anyway, if this SUM DDM value is actually useless for aviation purposes, we could think about ignoring it.

Correct (from a receiver view, not necessarily for ILS/LLZ check view). Are you sure the sum is for DDM, couldn't that be the sum of DM (SDM also part of Annex 10)? If this is not the case, then I don't see the purpose, but just a comment: DM are dimensionless ratios independent of actual course or clearance power, adding them directly could be ok. Just a guess.

Yes, I'm sure. They specifically asked for individual DDM (course and clearance DDM), combined DDM, SDM, and some other parameters. My guess was that the function f(·) would also depend on the original power from each component, so one DDM value could somehow predominate over the other if the power difference between the signals is big.

I'm happy with your first post, if you convert it to an answer I can accept it. If I'm able to get more information I will append it here afterwards.

I found a case of using the sum of DDM, which is relevant to analyze the DDM vs LLZ antenna array azimuth (source). As visible the sum is likely a simple sum (-.4 to +.4 in the on-course region, full scale on each side, then loosing accuracy after +/- 40° from centerline till 1st sidelobe -- an azimuth where the clearance signal prevents using the course beam anyway).

I think that is the kind of output they also expect to obtain. I had the chance to try Rohde demodulator and have several DDM pairs values recorded (course and clearance) and its resulting sum DDM, but still not sure how Rohde compute this sum value though. Thank you for the referenced document, @mins.

I don't think you're supposed to just average the two together somehow by themselves. The two signals are designed to be used in different zones and in practice have very different signal strengths at any point on approach.
From EVALUATION OF INSTRUMENT LANDING SYSTEM DDM CALIBRATION ACCURACIES [sic] by Dennis M. McCollum [PDF]:

The course pattern contains sidelobes that, without the clearance pattern, could cause an aircraft to select a wrong (sidelobe) course. Within the region of the true course (i.e., + 10 degrees about the designed procedural course), the signal strength due to the course array is greater than that from the clearance array. In the regions where the sidelobes exist, the clearance signal predominates. Airborne ILS receivers are designed to respond to the greater of the two signals.

This has to do with the background in processing these signals through analog means. Both the clearance and the course signals are within the passband of the receiver.  Since this is an AM receiver and DDM is more or less a ratio of 90 Hz to 150 Hz, if the clearance or course is much stronger than the other, the stronger one prevails.
So in practice measuring the course signal DDM inside the clearance region doesn't reflect what's done in practice, and I'd guess it probably isn't even a guaranteed behavior of the transmitter.  Do anything else instead in this region, like perhaps measuring just the field strength of the course signal.
But what about when slightly off the centerline?  Then you'd get a mix of course and clearance signals.  You could assume the ideal condition where a capture effect completely eliminates the weaker frequency.  Another approximation presented in the admittedly confusing paper "Current Issues in Demanding ILS Ground and Flight Measurement Environments" by Gerhard Greving and L. Nelson Sponheimer is
\[ DDM_{total} = \frac {DDM_{clearance}* CR^x + DDM_{course} } {1+CR^x} \]
Although I can't quite make out what precisely CR and X is here.
Depending on the application, it may be more realistic to model the amount of distortion expected or permissible due to clearance band interference, especially due to multipath reflections of that signal.  However, given your comments that probably won't help your specific application.

Perhaps you should think about why two frequencies are used. One thought is to prevent shut down of the ILS caused by reflections. In doppler radar this effect is called a hole, and happens at unique slope elevations depending on the specific frequency. Phase cancellation happens when the reflected energy is exactly 180 degrees out of phase, similar to the functioning of noise cancellation headphones.
Localizers shut down after 10 seconds and Glide Slopes are set to 5. I've seen a parked aircraft at the far end of the run way shut down a localizer by remaining stationary for more than 10 seconds.
Using an average value may be a bad idea when one of the signals is affected by phase interference.

Hi Javelin, thank you for your contribution. I didn't mention it in my first post but we are developing a measuring platform for ground inspection. So if it happens to be any phase interference, or other effects due to the environment, we actually need to measure how those are affecting the overall DDM.


text:
Why did Emirates order so many A380s?
According to the Wikipedia entry on the Airbus A380:

As of September 2018, Airbus had received 331 firm orders and delivered 230 aircraft; Emirates is the biggest A380 customer with 162 ordered of which 105 have been delivered.

Emirates ordered nearly half of all the A380s ordered. Why so many? Why aren’t other airlines ordering as much and adding the A380 to their fleets?

Maybe for the Haj?

Given that most of us don't sit in airline boardrooms it's difficult to say for sure why an airline favors one particular aircraft over another. But I'll have a go anyway. The A380 was initially marketed as having unbeatable costs per passenger compared to similar aircraft, i.e. the 747, so if you wanted to carry a lot of people a long way it was a logical choice.
In reality, those unbeatable costs only come if you can actually fill the seats. The introduction of the A380 coincided with rising fuel costs and the Global Financial Crisis. Less passengers and more expensive fuel helped the business case for heavy twins such as the 777, 787 and now the A350, and most airlines have preferred those types to the A380.
Emirates love the A380 because of some fairly unique circumstances:

Emirates operates a hub and spoke model in an excellent geographic location. It has its main base in Dubai and most of its business comes from connecting passengers through this one city - i.e. passengers travelling between Asia, Africa, Australia and Europe.
Emirates carried 58 million passengers in FY2017-18. How do you carry this many people through one airport, without running out of space? The answer is in bigger aircraft (and soon a second, bigger airport). Other airlines with such passenger numbers usually have multiple bases, and more point-to-point operations.
Finally, Emirates is less sensitive to extra operating expenses than other airlines due to its low cost base. This is largely thanks to favorable government conditions (such as labor and tax laws). Some even argue that they receive outright subsidies from their government.

I don't think Airbus pushed the efficiency figures that hard. Everyone knew they only applied to the densest configuration that was never ordered. Rather, the sales pitch was (and it certainly applies to Emirates) more that it has the most comfort: suites, showers, bar, all those 1st class/business perks that can't be matched on another aircraft. And like with most full-service airlines, this is the base that makes money for them.

The A-380 was designed with the hub-and-spoke business model in mind, which makes it a perfect fit for Emirates.


text:
Are you required to disclose medical conditions to your flight instructor?
When talking with a local flight school about my interest in starting training, I started asking questions about how the AME process works. The flight instructor then asked me if I had any specific medical issues. Are you required to disclose any health information to your flight instructor? What about if the issue(s) could be disqualifying? Would you get in trouble for lying to the instructor (to avoid judgement or maintain privacy) but NOT lying during the AME?

When it comes to the AME, you must disclose everything fully and completely.  Failure to do so may void any license and insurance and expose you to extraordinary civil and criminal risk.
When it comes to your flight instructor, who is not a medical professional, you do not need to disclose the specifics of your situation.  Saying, "I have concerns about passing a Class III Medical Exam due to certain conditions" is sufficient, and is not the same thing as lying.  Do not claim you are healthy when you know you are not.
Your instructor may decide not to continue training until a physical is passed, or he may decide just to be a little extra vigilant during training, and delay certain elements or maneuvers depending on the information you choose to provide.
For example: If you choose to disclose vertigo problems, he may avoid steep turns until medical clearance.  If you choose to disclose vision issues, he may avoid night-flight.
Regardless, you will need a medical before your first solo flight.
Do not lie to your instructor, but that is not the same thing as disclosing full details of your health with a non-medic.

Wouldn't it be also wise to disclose things that can kill you like "I have nuts allergy" or treatments that can kill you in case of emergency?

Wise? Yes.  Required? No.   The question is about what is required.

@abelenky I read this as one is requred to disclose all relevant infromations to allow [flight instructor] to assess one's ability to fly a plane safely. Personally I add "Better safe than sorry" or "If in doubt, cross out" to the equation. Detailed medical history is not a relevant information; "I am colorblind" is.

The answer is the same:  You are NOT required to get into your medical details with a flight instructor if you do not wish to.  You may choose to be general about a problem, such as "I have vision limitations", or be completely opaque: "I prefer to discuss medical issues with an AME".   There will be no legal or administrative repercussions for not being forthcoming with an instructor about medical issues.

@abelenky – the question shows initial inquiries about starting the training. Possible consequences of being opaque may lead to instructor declining the entire training until a clearance – just being opaque, too. (Of course, there is nothing wrong in it. It is just a difference between "hard" and "soft" approach from both sides.)

@abelenky I believe that instructor is NOT required to train someone if he is not sure it is safe. Actually, as far as I understand, he is required not to allow someone to fly if he has any safety concerns. Freedom not to disclose medical details comes with a price, if used.

@Molot:  Did I even remotely suggest otherwise?  I explicitly said the instructor may decide not to proceed with training.  But the student is still not required to disclose medical details to a non-medic.

There's no legal or regulatory obligation to tell your instructor about medical conditions as others have said. There may be rare cases where there are insurance considerations the flight school must take into account, in which case they should explain that.
There's good reasons to be open, however:
 - Not disclosing a medical condition could increase the risk to both you and your instructor, depending on what that is. The more the instructor knows about you the more they can look out for the specific issues a medical issue may raise
 - Training works better if there is a rapport and trust between the instructor and student. Lying to an instructor is a breach of trust, and could damage the relationship.
Think of it this way: how would you like it if you were an instructor and found out a student wasn't telling you he/she was prone to panic attacks? And you found out on final approach when the student suddenly went rigid, or worse pulled back on the controls and put you both in a life threatening situation? You'd want to know so you could make an informed choice on whether to take that student on, and if you did you'd probably elect a different training regime, one with more gradual steps.

There is no obligation to disclose anything to your CFI, just your AME. That said, your CFI may have useful advice about common problems, if you're willing to talk about them, and they may suggest delaying relevant parts of your training until thosr problems are resolved by your AME.
If a CFI (or anyone besides your AME) asks a question you don't want to answer, then tell them that, rather than evading the question or lying (even if only by omission), and they should respect your privacy.  Just knowing there's something they don't know is good enough.
If your flight school requires medical forms, then IMHO, find a new one. All they need to know is whether or not you have your medical certificate.

Flying clubs sometimes have more through medical questionnaires.  Some are for insurance data collection, and others are for risk reduction.

Some CFIs have more medical background than others, however they are not in a position to do any medical risk evaluation, as much as the FSDO inspectors might bug them for information on a student (when investigating).

@mongo: I've rented from FBOs, flight schools and flying clubs, and none ever asked for anything other than my medical cert.  No CFI ever asked me medical questions either, though I have asked them for advice on specific issues--as pilots who've dealt with the FAA longer than I have, not specifically as CFIs.

I have first hand experience with several flying clubs, and some of them have rather extensive questionnaires.  They don't ask you fine medical details, but one question which raised my eyebrows was whether one had received in-patient medical care in the last 10 years.  My student was a mother at that club, and she thought the question was potentially discriminatory, as most women who are mothers have been an inpatient.  The membership coordinator told me their insurance agent or underwriter asked that question.  More common questions are on alcohol and drug treatment and criminal convictions.

At this stage, when you are just talking about maybe starting to learn to fly, this person is not acting as your flight instructor. He's just a person giving you information about a process. You aren't under any legal obligation to disclose anything to him.
On the other hand, flight instructors often have a decent knowledge of the medical requirements to fly, and might have been able to give you a good opinion on whether any particular condition is disqualifying.
At a later stage, when you are actually taking instruction, it's probably a bad idea to withhold useful information from your instructor. It is likely that a flight school will make you fill in a form which asks about medical conditions, and lying on that would be a very bad idea.

The reason he asked that is because he thinks you asked an XY question, and thinks the "X" is "I have a medical problem that I fear might fail me on my medical". So he is asking only to answer your query, and he's not wasting time on the Y, and taking the shorter path to X.  Not his first rodeo...
As such, he's listening for relevant medical concerns likely to fail you, i.e. That could affect your safety to fly.  It would be an "overshare" to mention your excema, HIV status, enlarged prostate, well-managed cancer, eidetic memory, gluten allergy, or need for Viagra.
So answer the X: say why you think you'd have trouble with the medical.
You can always trot out the old "asking for a friend"... But then, expect to have an instructor who takes precautions against you having that problem in flight with him.  Really, a lying relationship is not one you want to have in the cockpit of a plane.

I can positively say that the conversation did not go as you describe. The conversation was about requirements to get a pilot license, which included the AME. I asked about the "process" in general terms (where to take one, cost, ect...). He was the one who brought up the exam details where he then asked me the medical questions.

i wan't there, but I can't see how you would frame a question about the process without it opening the door to his query.  It isn't really people's habit to give long general overviews, if they think there's a more easily answered, more specific question underneath it.


text:
I wonder if it's possible to make a "compressed air" turbine engine
I wonder if it's possible to make an efficient turbine engine that uses only hot compressed air to move but only that, meaning there is no ignition involved. To put it simple can we use compressors like turbo or superchargers to make a small turbine engine that will be able to move (not lift) 100+ kilos at high speed, well lets say around 40km/h (25 m/h)? I've studied it a bit and to actually know i need to make it but before that i thought to ask people that know certainly more than i do. Also if you can think of a way to do it i'd love to hear it cause iv'e thought of something but it might not work (i guess that's the fun of it tho doing tests and rebuilding and stuff). Ok, in addition to all that let's say that power for this comes from batteries and it's meant to work for short periods of time.

Are you proposing a turbine engine that doesn't use any fuel or other type of input energy at all?

The way you use "turbine" is very confusing. Turbine is the thing that converts high pressure gas into motion. Compressor is the thing that converts motion into high pressure air. The way a jet engine works is the combination of the two. When you burn fuel, the turbine/exit side has more gas volume and velocity than the compressor/entrance side and you generate thrust. If you want to skip the turbine and use a electric motor or a piston motory, it's perfectly OK.

I'm totally confused here. Do you want a electric-motor driving a compressor, or do you want compressed air to drive a gas turbine, or something else? Turbofan is basically turbine driving a fan with hot high pressure gas, which comes from a device called gas generator, which uses another turbine to drive a compressor to compress air to burn fuel with to generate hot and high pressure air.

Why would you want to do this, instead of simply hooking your electric motor to a propellor, as with drones &c?  I'm pretty sure it would be extremely inefficient to use batteries to heat & compress air, then push that through a turbine.

Your comment to my answer: " The energy will come from batteries," and your recent edit completely invalidates my answer, therefore I am deleting it.  The comment of @jamesqf is the correct answer to your new question: if you have batteries, just hook up to an electric motor and a propellor.  Using a compressor and a turbine with an electrical resistive heating in between would work, but it would be ridiculously inefficient.

I gave an upvote for the thinking. No one starts out an expert here, but will never get anywhere without trying, and, importantly, communicating ideas.  Too many bashers here who do not appreciate learning and thought process.  There are a LOT of methods to propulsion, yet many do not realize how efficient flapping wings are!  Keep working Anton!

Thank you Robert i really appreciate that! And to answer some other questions there will be a motor driving the compressor (now the type of the motor doesn't Matter tho DC is more efficient with batteries rather than converting DC to three phase AC for an AC motor) and of course there will be input energy (batteries) but im not going to add extra energy into the system when the batteries die it stops working

@anton siro: Re "motor driving a compressor", you've just invented pneumatic tools :-)  There are a lot of reasons to use them (see e.g. https://en.wikipedia.org/wiki/Pneumatic_tool ) but efficiency isn't one.  Compressing a gas is not 100% efficient, nor is the tool itself, so you loose a good deal of the energy stored in the batteries.  You might do better using e.g. a scuba tank as your compressed-air source.

Well, ships have been using turbine engines powered by super-heated water since the late 19th century.  But you still have to have an energy source to heat the steam.  And it's no good for a "jet" engine since the whole point is thrust by accelerating air through the engine, where the turbine and compressor are there just to keep the cycle going.  It would only work for a turbo-prop or turbo-shaft where the turbine's job is to produce torque for doing the work.
Theoretically, you could have a turboprop powered with a steam turbine, or some other heated gas, but you still have to have an energy source.  Maybe some kind of weird and wonderful battery powered water heater, or a tiny nuclear reactor?  Then you also need a huge supply of water or other fluid or gas to heat up.
It is possible however to have a closed system that recycles the water used for the steam.  You then have pretty much a small nuclear power plant or nuclear sub.  It's theoretically possible though, to have a nuclear powered turboprop that could fly for months.  If it works for subs and aircraft carriers, why not, if you could make the whole thing light enough.
Actually, none of that stuff is really new.  There were nuclear powered aircraft concepts in the 50s, that weren't really practical.
The thing about turbine engines powered by kerosene is that it's still the most efficient way to convert potential energy to kinetic energy in a light weight and trouble free package.  50 years from now?   Who knows.

I see. still let's say we can run it with a big amount of batteries (or a small nuclear reactor) would just a small turbo or supercharger like those used in cars (with a hint of thermal expansion im talking about getting the air out even hotter and more "charged" you can say) give me good results?

To just heat the air itself with something, you would need to impart a crazy amount of BTUs of energy into the air to get the required expansion to create the required velocity in an air stream, and would still need a turbine/compressor to get and sustain the cycle because you have to pack a lot of air into a small space before you heat it.  I mean, you could probably create some kind of nuclear reaction right in the burner can of a jet engine although you would have radio active exhaust.  The basic issue is the sheer amount of energy and mass involved to move something by a jet exhaust.

However, you CAN make a turboprop or turboshaft engine that runs on compressed air.  It's done with piston engines all the time and there are compressed air cars.  For a turboprop/turboshaft, you'd need one mega pressure air tank however.  And you'd still need an energy source to compress the air in the first place.  No free lunch under the sun....

I see thank you very much!

The idea falls foul of the law of thermodynamics.
The chief problem is that you seem to convert electricity (from the battery) via thermal energy (heat) to mechanical energy. This cannot be efficient. The amount of thermal energy that you can convert back to other forms of energy is limited by the [Carnot efficiency](https://www.e-education.psu.edu/egee102/node/19420.
As @jamesqf points out in the comments, you can skip the whole thermal step and just have an electrically driven propeller. By not heating the air, you avoid the inefficiency.
Now turbine engines running on kerosene are also limited by this same Carnot efficiency. I just told you it's bad, but why then do planes still burn kerosene? It turns out that kerosene has a much higher energy density than batteries. This means the plane can be much lighter at take-off, which compensates for the thermal inefficiency.

@jamesqf gave the correct answer in his comment.  Let me elaborate on why it would be inefficient.
Typical turbofan engine energy path is like this
chemical energy (fuel) -> thermal energy (burning fuel) -> mechanical energy (low pressure turbine shaft rotating = fan blades rotating) -> mechanical energy (large volume of air accelerated out the back of the nozzle).
So 3 different conversion steps. Each step is not 100% efficient. You lose a decent amount of energy at every step. So the more steps there are the worse.  Your proposed situation is something like:
chemical energy (batteries) -> electrical energy -> thermal energy (heating the air) -> mechanical energy (low pressure turbine shaft rotating = fan blades rotating) -> mechanical energy (large volume of air accelerated out the back of the nozzle).
This has more conversion steps than a typical jet engine.  It will be less efficient.  The alternative path proposed by @jamesqf is
chemical energy (batteries) -> electrical energy  -> mechanical energy (propeller rotating) -> mechanical energy (large volume of air accelerated past the propeller).
Do you see how this has one less conversion step?  you just go straight from electrical to mechanical energy with no thermal step in between.  Less conversion steps is better.

I see now. So i can just use a motor and be more efficient and have the results i want. well i'll see what i'll end up doing but everyone was so helpful and made me think of stuff that i didn't have in mind until now, thank you very much!

A turbojet with 'no ignition involved' is in principle possible, and it has been put into practice in the 1950s, in working prototypes of nuclear powered propulsion units.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19640019868.pdf
https://en.wikipedia.org/wiki/General_Electric_J87

As I understand it you want to have a compressor creating compressed air that exits in a high-speed jet, thus causing thrust, but you want the jet to be comprised only of air, not of combustion products.
That describes the air that is accelerated by the fan in a fanjet engine, which provides a substantial portion of the total thrust in such an engine.
Or if you prefer, rather than powering the fan by a turbine, you could power the fan or compressor by a piston engine.   The "motorjet" concept (see https://en.wikipedia.org/wiki/Motorjet ) used in the The Caproni Campini N.1 -- ( see https://en.wikipedia.org/wiki/Caproni_Campini_N.1 ) might seem to approximate this idea, but in the "motorjet" concept the compressed air IS mixed with fuel and ignited after compression, to provide more thrust than would be provided simply by allowing the compressed air to exit the nozzle without ignition.
There was at least one piston-driven "jet" engine concept in which the air was NOT ignited after compression -- see for example the Coanda-1910 (see https://en.wikipedia.org/wiki/Coand%C4%83-1910 ).  This plane apparently never flew, but a similar engine was used to drive a snow sledge.  That seems to be a good match to what you are envisioning.


text:
How to fly a quick return to origin after takeoff
If I want the shortest traffic pattern to play touch and go or I got a emergency right after liftoff but the engine is still working, I just want to get back to ground as soon as possible, what is the best flight profile to get back to the takeoff runway?
Question 1: Is the below lateral path(that is there is no straight segments during the two 180 degrees turn) the best route to do a quick return to the original runway after takeoff, considering the time and safety? I think it is because it helps avoid taking off traffic, fully utilize the runway length to do a headwind landing.
Question 2:How to fly the vertical profile, like to climb to what height? I think should climb to the pattern height to clear the terrains and other traffics.
Question 3: At which point should I start the descent? Should I deploy all drag devices like full flap and idle the thrust to maximize the descent angle as soon as I start the descent?

Are they engines running? Is there wind to consider? How long is the runway? What plane are you flying? There are a lot of variables here that will change the answer you may want to specify the situation a bit more.

@Dave, the engine is still running, and I want to fully utilize the runway length to do a headwind landing.

Climb to pattern height, do a 180, land down-wind. What is the emergency? If it isn't an emergency and you just want to get down, fly a normal pattern.

@Ron Beyer: Is there even an emergency involved here?  Looks to me like practicing touch & goes.  (When I was doing that, I'd make it to pattern altitude about midfield on the downwind leg.  C-150s don't climb all that well :-))

If all you care about is speed you don't climb at all and fly the downwind at full power in ground effect. But I guess that doesn't square with the "safety" requirement in the question :)

Why wouldn't you just fly the pattern? Unless you're on fire just stick with what you know.

The "safety" part seems extremely subjective and situation-specific.  Is the airport in a wide-open field or are there things you wouldn't want to hit in some areas?  Likewise how high to climb seems largely a matter of pilot preference.  And how steep to bank in the turns.  Obviously you are going to prioritize keeping the airspeed up rather than achieving a high climb rate, at least on the downwind leg-- but all in all I'm having trouble seeing how this is an ASE-worthy question.

Multi-part questions invite being closed, see for example https://aviation.stackexchange.com/questions/88256/in-the-us-what-radio-frequency-or-frequencies-should-be-used-by-glider-pilots-a

With an emergency, the objective is not to fly the quickest pattern possible, it's to be back safely on the ground as soon as possible, with the greatest probability of success. If you save 10 seconds by doing something that substantially increases the risk of wrecking the aircraft because you flew it into something, that's probably a poor tradeoff.
In the pure "minimum time possible" scenario, you want to minimize distance flown & maximize speed (up until the point you're slowing down to land), which means things like steep angles of bank, minimum time spent climbing, rolling out of your final turn right over the numbers, and so forth. So you fly the pattern at full throttle at a really low altitude, with a continuous turn to final at a high angle of bank, chopping power and descending so that you simultaneously roll out of the turn and reach your target landing airspeed all right over the numbers at minimal altitude, with no left/right offset. Cool airshow trick if it works, but an awful lot of opportunities for things to get off the desired parameters, at which point your choice is to go around & try again (false economy in time "saved" with the aggressive pattern there) or else to try to salvage a bad setup, which - especially with the added stress of the initial emergency - is a recipe for destroying the airplane yourself and achieving the worst possible outcome from the emergency situation... which might well have been survivable with a more controlled, less aggressive flightpath.
Unless it's something you're highly proficient in, (i.e. you regularly practice exactly this for your airshow routine), the absolute minimum-time pattern described above is not  what reasonable pilots would choose, even with a cabin filling with smoke and screaming. They probably wouldn't fly a leisurely, wide pattern like initial training, but avoiding things like stalling, flying into the ground in a moment of distraction, or being so high on final you land long & overrun the pavement are all higher priorities than saving those last few seconds.
If the situation really is so dire that you absolutely must land right now, then (in a light aircraft, at least) perhaps it's time to consider landing straight ahead on a road or a field or a body of water, rather than returning to the departure runway.  Scenarios requiring that much urgency, though, are more the stuff of imagination than of common occurrence.

The quickest and safest way is to fly the standard pattern, especially if you are at an uncontrolled airport.  Why?  Because that is where everyone else is looking for  you to be.  Per the Airplane Flying Handbook Chapter 7 states:

compliance with the basic rectangular traffic pattern reduces the
possibility of conflicts at airports without an operating control
tower. It is imperative that a pilot form the habit of exercising
constant vigilance in the vicinity of airports even when the air
traffic appears to be light.  Midair collisions usually occur on clear
days with unlimited visibility. Never assume you have found all of the
air traffic and stop scanning.

If you are near an airport you don’t want to be somewhere where other pilots aren’t looking for you or expecting you to be!
On your upwind leg you should climb to between 800 - 1,000 MSL before starting your turn to crosswind. Continue climbing to your pattern alititle (Field elevation + 1,000 feet).  Turn to your downwind leg so that the runway is off of whatever reference point your CFI has told you for the aircraft you are flying.  (About ⅓ of the way up my wing in a PA-28-181).
In a normal pattern you should start your descent when the runway is about 45 degrees off your shoulder. How many flaps you should use and when to deploy them depends on the situation.  Gusty winds land with less flaps or even no flap, calm conditions use full flaps.  General rule is you do 10 degrees on downwind, 25 degrees on base and full on final. But depending on the conditions, use your flaps to help you control your speed as necessary.
If you’ve done short approaches with your CFI you can do those as well instead of flying the standard pattern.  Keep in mind, if you are at a tower controlled field a short approach is not part of your option clearance you must ask the tower to do a short approach.  In that case when you are abeam the numbers, you put your power to idle, start turning to the runway and trim for best glide.  Drop in your flaps as needed to help you maintain proper glide speed and descent angle.  Should try not to put in full flapt till you're on final and have the runway made.

"climb to between 800 - 1,000 MSL" I guess you meant AGL?


text:
How does a remote pilot land a fixed-wing UAV?
How does a remote pilot land a big fixed wing UAV, whose takeoff weight could be several tons and have to land at a airport with runways? I saw in the TV, these big UAV normally has on-board cameras and its remote pilot work at a station with displays. Is it manual or auto landing? If it is a manual landing, is it similar like manned aircraft pilots to set up the visual contact with the runway and determine the aircraft position in space relative with the runway based on their experience or they have some landing aided system? How they resolve the time delay issue that the image they see thru the onboard camera could be taken seconds ago?

that's a lot of questions, and (unless you restrict it at least to a specific model) way too broad.

I though UAV autoland the same way airliners can land on ILS cat III runway.

There's a wide range to techniques. In the hobby world, it's much like landing a full-size plane under VFR, you fly a circuit and glide path. Flaps, side-slip, cross-wind, retractable undercarriage, etc can all be used. The difference is that you have to judge the runway centre-line from some distance off to one side, which requires a lot of skill and practice. Also wind-sheer, gusts and unevenness in the runway surface are magnified by the scale. Fortunately the light weight allows models to handle landings that would wreak the full-size.
At the other end of the spectrum, large UAVs can land autonomously, similar to an airliner auto-land, using all the electronic aids of a modern runway.
In the middle are small UAVs, operated away from a runway. Small, slow UAVs can just circle a GPS position with the motor off, gliding until they reach the ground. Faster UAVs fly into nets or a vertical arrestor wire - again autonomously.
For completeness, I should mention that there is a specific branch of model competition for landing on a simulated carrier deck, with an arrestor wire.


text:
How a takeoff decision point(TDP) for vertical takeoff vehicle is defined?
For a vertical takeoff vehicle like a helicopter, how the takeoff decision point is defined or computed? Look at the snapshot below, seems the height of TDP is related to the rejected takeoff distance?  What is its relationship with obstacles and rejected takeoff distance?

Short answer
The TDP is part of the takeoff profiles provided by the manufacturer for any category A helicopter. Its height is selected based on helicopter performances determined by flight testing. Profiles includes a back-up takeoff used for small takeoff areas:

Source
In this profile, the helicopter first moves backward to get away from obstacles, following a slope which angle is provided by the manufacturer. Height of the TDP can be increased up to a maximum, in order to meet both the minimal rejected takeoff distance and the minimal clearance for one engine out climb (amber curve), provided the rearward flight is remote from obstacles below (safety zone):

Source

Performance class and helicopter category
Helicopters are required to operate under a performance class, which determines how safe the operation is in case of single engine failure (OEI = one engine inoperative). TDP is associated with performance class 1 (PC1), which imposes a safe takeoff phase, with a safe climb in OEI after passing the TDP, and a safe rejected takeoff (RTO) prior to the TDP.  PC1 TDP plays a role similar to V1 for in balanced field takeoff for planes.

Source
PC1 operations are usually required by local regulation for 20+ passenger helicopters  and/or IFR operations.
Helicopters belong to two certification category: A and B. A helicopters are those able to perform in PC1. For these aircraft the manufacturer provides takeoff profiles including a TDP. There are often three profiles: Runway takeoff where the helicopter leaves the ground in a short vertical climb before flying forward over a clearway, back-up takeoff where it flies up and backward until reaching the TDP, and then flyes forward above obstacles, and a vertical profile to takeoff from elevated helipads (like tower roofs) with low visibility on the lift off area.
The principle with these profiles is the pilot is always able to abord the takeoff before reaching the TDP, and always able to climb after passing the TDP.
By using the back-up profile (example), the helicopter can increase its height while maintaining the RTO distance to the FATO (final approach/takeoff area). After reaching the TDP, the helicopter can fly forward clear of obstacles to gain speed and reach VTOSS.
Regulation for Category A in the US
As an example of regulation requiring the TDP to be defined, let's take US/FAA. This regulation is based on recommendations from ICAO Annex 6, Part 3, from which this diagram is taken (10.7m = 35ft):

From FAA AC29-2C:

Category A takeoff performance must be scheduled so that:
(1) If an engine failure is recognized at the Takeoff Decision Point (TDP) or at any point in the takeoff profile prior to attaining TDP, the rotorcraft must be able to land safely within the established rejected takeoff distance.
Flight testing to determine the Category A rejected takeoff distance is very similar to height-velocity testing and should be approached with caution.
(2) If an engine failure is recognized at the TDP or at any subsequent point in the Category A takeoff profile, a continued safe climb-out capability must be assured. The continued takeoff for conventional Category A runway profiles is designed to allow acquisition of the takeoff safety speed (VTOSS) at a minimum of 35 feet above the takeoff surface and a positive rate of climb

Thanks for clarifications, if I understand correctly that higher obstacles requires higher TDP to clear the obstacles, higher TDP requires longer reject distance, so how the reject distance could be computed then?

TDP is part of the manufacturer takeoff profiles. For an example see page 7. The height can be increased, and a back-up takeoff can be used if this is not sufficient. With the later, the TDP can be moved along a slope, which angle is given in the profile. This allows to find the location meeting both obstacle clearance and rejected take off distance. More examples.

Excellent answer, but really isn't the graphic and explanation contained in the question a condensed version of this?  (you even included three very similar versions of the same profile view!)

@MichaelHall: Thanks for the feedback. I've restructured the content.


text:
Why there is a descent segment during helicopter takeoff?
I am reading some regulations about vertical takeoff vehicles like a helicopter and there is some takeoff path is defined as below, and I am curious why there is a descent segment in its takeoff path? Is that a typical procedures that pilots pitch down to accelerate during takeoff?
Vtoss: Takeoff Safety Speed?
TDP: Takeoff Decision Point

Can you find descriptions of what the TDP and the VTOSS points represent in the diagram you pasted? Understanding those may provide some insight into what's going on with the various segments.

Related: Why don't helicopters always takeoff from a hover out of ground-effect?

Please share the source of your image.

These diagrams are used to depict the possible trajectories the helicopter can fly after a single engine failure. The pilot must ensure that there is sufficient obstacle clearance for that case.
This is for helicopters with multiple (i.e 2) engines. The take-off paths shown, are considering a failure of an engine at (just after) the take-off decision point (TDP). At engine failures before the TPD, the helicopter should be able to land safely at the final approach and take-off area (FATO).
Hovering and flying at low speed requires a lot of power. In case an engine fails during hover, the helicopter may not be able to accelerate forward while maintaining a positive vertical speed (i.e. climb). The optimal speed for climbing is the take-off safety speed, VTOSS. In order to transition between the hover and the climb at VTOSS, the pilot may need to trade height for speed initially. When VTOSS is reached, the helicopter can start to climb again.
The third diagram shows a vertical take-off in a confined area. In order to do so the helicopter need sufficient excess power available, even after a single engine failure. This usually limits the maximum take-off weight for such operations.
The horizontal distance between the TDP and the point that the helicopter starts climbing at VTOSS is called the take-off distance required.

That whole "engine out" factor makes a lot more sense out of this!


text:
Why has the range of movement of the control surfaces changed over the past year?
During the annual inspection on our glider, we discovered that the maximum downwards extension of the right aileron (i.e. full left stick) was outside the manufacturer's tolerance. The measured value was 32mm and the manufacturer allows 40mm ± 5mm.
What are the possible causes of a change in the geometry of the system such that the ailerons no longer move in the range they did last year?
For reference, the glider is a 1983 Schleicher ASW19b, with standard l'hotelier control connections and aluminium push rods over bell cranks in the fuselage and wings.

We found the problem. The control stops are under the seat and are made of plywood. It looks like at some point in the past someone had added a small layer of plywood to reduce the control deflections but that over time the glue had deteriorated or the wood had swollen, so that there was now too much stop. Removing the extra ply and sanding the glue back to the wood fixed the problem.

We found the problem. The control stops are under the seat and are made of plywood. It looks like at some point in the past someone had added a small layer of plywood to reduce the control deflections but that over time the glue had deteriorated or the wood had swollen, so that there was now too much stop. Removing the extra ply and sanding the glue back to the wood fixed the problem.

plywood does tend to swell when it gets moist.

Possibly an obstruction somewhere, causing it to not move through its full range because it gets blocked by something.
Or a cable that's become too long (stretched...) causing full deflection to  no longer move the surface through its full range of motion.
My guess if the aircraft is regularly cleaned and inspected in between flights is the latter, as it's something that's creep in slowly and gets worse over time.

Thanks for your answer! There are no control cables in this case (only the rudder). Obstruction is a possible and worrying explanation, I will send a camera along the control circuit.

Coming to this question late, but a recent experience I had might suggest a reason.
While assembling our club's Open Cirrus last weekend with another pilot, we noticed the gap tape on the elevator was missing.  My compatriot applied new tape while I attended to other assembly items.  After we completed the rigging, we did a positive control check, and, to our surprise we were not getting full deflection on the elevator.  After some examination I discovered the issue...the tape was applied in manner that prevented the elevator from moving completely.
When you apply tape to an elevator (or aileron) you have to apply the top tape with the control surface down and the bottom tape with the control surface up, thus allowing full movement.
Is this your issue?

We have experienced this in the past. In some cases the tape can shrink over time, so you get full deflection when it's first applied but weeks or months later the tape prevents full movement. You have to make sure there is a bit of slack in the tape when the surface is at full deflection, and it's worth checking this at every DI.

It's very hard to say exactly what is wrong in this case, but much if it is worrying. As it is only one of the ailerons which is not deflecting that does narrow the possibilities. It could be that there is an obstruction which is preventing full deflection, this could be something as simple as foreign object debris working its way into somewhere, or something has come loose. A bell crank could be loose and shifting rather than transferring all of the movement. One of the linkages in the pushrod system could be loose. The wing could have flexed somehow, changing the length of rod needed to deflect the aileron fully.
Try having someone hold the stick still while you wiggle the aileron, if you get play in it then it's likely a loose bit somewhere. In any case I would get some professional help on this if you haven't already.

Thanks for your insight! The other measurements aren't perfect (don't have them to hand) but are within the tolerance. The tolerance for the downgoing aileron is less (±5mm) than the upgoing aileron (±10mm), which is to be expected with differential ailerons such as these. So it's possible that the other aileron is affected in the upgoing sense, but is still within the limit.

Will also check explicitly for play, but I would have hoped that we would have noticed 8mm of play! We tried loading the wings by hand in order to induce the sort of flexing length change you describe, but the deflections of the ailerons did not change.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Tu-144 vs Concorde: which one of the two carried passengers first?
I know that the Tu-144 had the first prototype flight and it also beat Concorde in reaching supersonic speed, but what I am really curious to know is which design carried  passengers first (not crew and test engineers only) as a commercially operated aircraft. Is it still the Tu-144 or was it Concorde? Could anyone offer some insight, please?

Besides crew and test engineers it is quite possible that several other people flew on Concorde prior to the official launch of commercial service, such as company executives from the manufacturer or one or more airlines. But it would probably be difficult to find any published records of this. And anyway the question specifies flying as a commercially operated aircraft, which would mean flights carrying paid passengers or cargo.

Concorde was first by almost two years:

Aircraft
Maiden Flight
First Commercial Flight
Source

Concorde
2 March 1969
21 January 1976 (London → Bahrain & Paris → Dakar → Rio de Janeiro)
simpleflying.com

Tu-144
31 December 1968
1 November 1977 (Moscow → Alma-Ata)
Kazan National Reserach Technical University

The Tu-144 commenced commercial on the 1st of November 1977 (according to Sinsheim Museum)
According to some sources the first commercial flights of the Concorde took place on the 21st of January 1976. (On that day two Concords flew with flight numbers AF085 & BA300)
So the Concorde was the first to transport "real" passengers.


text:
Where does it say that type certificates are required?
I am doing research and looking for a regulation (from FAA, Transport Canada, ICAO or anywhere else) that explicitly states that a type certificate is required for aeronautical products (aircraft, aircraft engines, aircraft propellors). I have looked around on google and at the CARs and FARs but haven't found it yet.
Can anyone help me find a specific reference to this regulation?

"For aeronautical products"? What?

@RyanMortensen Aeronautical products are aircraft, aircraft engines, and aircraft propellors (https://laws-lois.justice.gc.ca/eng/regulations/SOR-96-433/FullText.html#s-521.01) (https://www.law.cornell.edu/cfr/text/14/21.1)

Sorry, I was thinking type ratings; disregard.

I guess I was thinking about it the wrong way. I was hoping for a single regulation to cover it. These sections of the FAR seem to be enough to say that type certificates are required for aeronautical products.
14 CFR §21.45 states the privileges bestowed to type certificate holders including the ability to obtain airworthiness certificates for aircraft, install engines and propellers, obtain production approval or replacement part approval.
14 CFR §21.6 states the need for a type certificate in order to manufacture new aeronautical products
14 CFR §21.9 states replacement and modification parts need to be produced under type certificate
14 CFR §21.132 states that a type certificate is necessary in order to be eligible for a production certificate.
14 CFR §21.183 states that in order to get an airworthiness certificate the aircraft must conform to its type design.
There are probably more examples in other sections. Any other answers appreciated.

And of course, at the component and parts level, parts have to meet a Technical Standards Order (TSO) and someone making the parts has to be granted Part Manufacturing Authority (PMA) to be able to ship them to the manufacturer (unless the manufacturer does its own conformity inspection) or to an airline.

@JohnK  TSO is entirely optional. It does however, provide both design and manufacturing approval. But the TSO part must also be included in the aircraft TC (or an STC) for it to be used on the aircraft. If the part's design approval is the TC, then a PMA is required to manufacture it (the design belongs to the aircraft manufacturer) and it can only be sold for use on that particular a/c model. A TSO part's design belongs to the TSO holder. They can sell it to any aircraft manufacturer that wants to use it (subject to them certifying it as part of their TC).


text:
What is the proper protocol in the US regarding abandoned aircraft not deemed safe to fly?
Security forces in Guatemala detected a plane entering airspace on 4 Nov 2021. They followed through and found it abandoned, with evidence that it transported illegal drugs. After an assessment by military technicians, Guatemalan government authorities ordered the burning of the aircraft one day later because it was not deemed safe to fly (unclear if it was  because of the terrain or other). Not mentioning this controversial way of disposing of such major evidence so soon, my question is, what is the proper protocol in the US regarding abandoned aircraft of recent model that are not deemed safe to fly? Are there FAA regulations about the matter? What US authorities would do in such scenario as the one in Guatemala? My question specifically pertains to aircraft.

That's more a legal question about property seized/confiscated by police, the fact it's an aircraft likely has no impact.

I agree, voting to close.

I am asking specifically because the aircraft was deemed unsafe to fly. So my doubt is if the FAA has rules about this, do authorities do the same thing to aircraft that are deemed not safe to fly.

As the answer below demonstrates, there are some unique aspects to aircraft that don't apply to other things that law enforcement might seize.  Voting to leave open accordingly.

“Seized” and “abandoned” are completely different legal categories.  But again, they have legal definitions and disposition of property will depend on jurisdiction.  I am confident in saying that nothing in 14 CFR deals with these distinctions.  Standing by my vote that this is a more a legal than aviation question.

Too much bureaucracy for a Q&A site. I just finished a course on Government Administration as to why bureaucracy is not a good model of running things, but rather a flexible management model should be used; in this case, flexibility to favor freedom of information. But I'm happy with the answer received.

You just gotta find the right place to ask!  There is a legal stack exchange…

@MichaelHall Hasn't it happened to you in bureacratic establishments, whether private or public, they send you from one place to another and back again?

At least put the question on hold and provide feedback on how to bring it to standard so it can be opened. Why close it at once?

Yes, I have had that happen, but this is not a bureaucratic establishment.  In fact, it is about the exact opposite!  It's the internet, nobody works here...  I understand your frustration, but I think it's misplaced.  Did you ask on the legal SE?  And did they close your question and refer you here?

@MichaelHall I haven't. According to the help guidance of this Exchange, it says ask about aircraft regulations, which is exactly what I did and yet my question was closed.

I'm not trying to discourage you, I'm simply telling you, (to the best of my knowledge and with a high degree of confidence) that aviation regulations don’t cover disposal of abandoned property.  The fact that the property is an airplane is irrelevant.  You wouldn’t expect rules on how to get rid of a rusty old oven abandoned on your front lawn to be covered in books about baking, design for UL certification of convection ovens, or under food safety regulations would you?  Please, try asking on Legal Stack Exchange...

@MichaelHall Ok, I will do that. The issue is that Guatemalan authorities are claiming that they destroyed the plane following FAA regulations.

Short Answer: If the case is closed and the plane is neither airworthy nor evidence used in a case where the death penalty was issued, the US government has a full process for destroying it (outlined here).
If the log books were found with the aircraft it may be recovered,  depending on the state in which they find the aircraft. In the US,  property seized by the government in drug related cases can, in some instances, be auctioned off. The issue with aircraft is that in order for them to be deemed "airworthy" (what I assume you mean when you say "safe to fly") you would need the log books to prove that the aircraft is compliant with all relevant maintenance history and AD's.
Often maintenance logs are not stored in the aircraft as they can get lengthy and heavy over time and there is no requirement to have them onboard. So if the government seizes an aircraft that say, flew into the country illegally, there are likely no logs with it. Factory overhauls of engines can reset this (for engine logs) but that can be costly. Reconstructing airframe logs can be quite a difficult (if not impossible) task. So again, with out the logs the airframe is likely prohibitively expensive to bring the airframe back to airworthy condition but it may be liquidated nonetheless for far less than an airworthy example. Similarly with out the logs you cant even part the plane out since you cant add valid parts tags to the parts without knowing the service history. Interior trim and other non airworthy related parts can be pulled and sold without the tags but thats not really where the value is.
Interestingly in this case the aircraft was seized before being delivered to El Chapo and according to the article will be auctioned off so they presumably seized it with the Log Books.

I don’t know why you say the airplane is worthless. Planes come on the market all the time with missing logs because they burned up, the owner died, or they were repossessed. The value is much less and it’s expensive to redo all the ADs but, in the US, Part 91 flying doesn’t have any limit on time in service for engines and parts. There are a few piston aircraft that life-limited parts, like Cirrus parachutes, but that can be dealt with by replacing the parts. There may be some oddball airframes with time-in-service limits but I’m not aware of any.

@JScarry I as always under the impression that generally going back through all the AD's and zeroing the engine out was broadly more expensive than a plane of similar vintage and condition. Im sure there are exceptions for rare airframes etc.

What is the meaning of AD?

@freethinker36; AD = Airworthiness Directive some are optional but some are mandatory and if that is the case the work needs to be preformed and a log book entry needs to be made.

@Dave For Part 91 flying there is no need to zero out the engine—TBO not a limiting factor. Fly it until it starts making metal/won’t pass compressions. AD compliance could be a problem on some airframes but with the insane aircraft prices right now its probably worth it if you get a good deal on the aircraft. As a data point, my 1968 Cherokee has 25 ADs most of which are just an inspection. A lot no longer apply because the part has been replaced: Carburetor, ignition. One requires replacement of oil hoses every 7 years so would have to be done. Probably no more than $3000 to comply with all.

@JScarry for another data point one of our clubs PA-28's was hit with the wing spar AD.... ...thankfully one of the members had a horse trailer and could get the wing to Ohio for us saving the shipping. But I understand your point I changed the verbiage a bit in the answer to make it more broad.


text:
Why is a rectangular wing with winglets not better than an elliptical wing?
Why is a simple rectangular wing with winglets not better than an elliptical wing in terms of induced drag and produced lift?

It’s an interesting information. I am curious to read the reference behind the description.

If using Prandtl's lifting line theory, then mathematically/analytically, ignoring issues of wing weight that lead to bell shaped lift distributions and other sorts of intrusions of reality (e.g., stall behavior) the elliptical wing with the elliptical lift distribution is optimal for minimizing induced drag given a fixed wing area.
You can get an elliptical distribution of lift from a rectangular wing via twist, winglets, or other mechanisms, but it will only be elliptical at one cL value. At other values, it will not be elliptical, and thus suboptimal.

I'm not sure what you mean by "optimal" and "can't be improved on" because a planar elliptical wing does not produce an elliptical lift distribution.

A wing with an elliptical chord distribution (and minimal sweep, minimal dihedral, and moderate aspect ratio) produces an elliptical lift distribution.

No, a planar elliptical planform wing definitely does not produce an elliptical lift distribution. (Twisted wings are a different matter.) This was known to Prandtl and his students as far back as 1937.
See, for example, among many dozens of other papers:
Peter F. Jordan, "Exact Solutions for Lifting Surfaces", AIAA Journal, Vol. 11, No. 8, 1973., pp. 1123-1129.
Peter F. Jordan, "On Lifting Wings with Parabolic Tips", ZAMM 54, pp. 463-477, 1974.

OK, I'll caveat my answer to what Prandtl's LLT infers.

@MikeY Re your answer, why would I want an elliptical distribution to begin with? Isn't this only the optimal solution for a finite wing, i.e. one where at the ends of the wing pressure from below the wing can freely travel to the upper side?
Couldn't winglets - if large enough and going in both directions - create a "barrier", effectively turning a finite wing into an infinite one?

@Lysistrata So what planform  of a wing without twist, sweep, dihedral, winglets ... produces an elliptical lift distribution? Can you post an image that contrasts it with an elliptical wing?

I assume neither of you can answer my questions?

@xnor, assume for a second that by putting a surface into the tip vortex you can improve performance. You should be able to put the surface anywhere in the vortex and see the improvement, as the vortex is symmetrical about its rotation. Up, down, or horizontal outwards. This means you can arbitrarily pick a point on a wing, and consider what is outboard of it to be winglet. So the question is, is there anything to be gained by bending the wing up?

There are some examples in D.W.F. Standingford's PhD thesis:
https://digital.library.adelaide.edu.au/dspace/handle/2440/19063
(Disclaimer: I assisted with several sections.)
Unfortunately, techniques like vortex lattice methods or Tuck's method aren't sufficiently accurate to produce "exact" elliptical distributions. I'm not sure if anyone has improved on that situation recently.

@xnor: People will answer when they have time. Don't start assuming your question is so important that we have to answer it within a day or two.


text:
What is the effect of moving a propeller closer to a wing?
Does it improve efficiency?
What if the wing is just a plate? Certainly increasing plate thickness will decrease efficiency.

What do you mean closer to a wing?  Along which axis? (ie moving a prop from nose to wing, or moving a prop mounted in front of a wing, back towards the wing, or moving a pusher prop forward to be close to the rear of the wing)

@tmptplayer in front of a wing, moving closer to the wing as in reducing the distance between the prop blade and the leading edge of the wing


text:
pre-departure sequence, how to increase number of flights in the sequence
If I have number of flights ready to depart (valid TOBT) if I want to increase the number of flights in the queue by adding flights in the gaps between any 2 flights whats the minimum seperation that should be taken into consideration?
example:
suppose I have 2 flights the first one is already included in the sequence and it has CTOT. the second flight is still not included in the sequence and has no CTOT(the origin and the des airport not in Europe) and I would like to add it before the first flight since I have time between its TSAT and its TOBT.
whats the minimum seperation time that allow me to add another flight?
TOBT => Target Off Block Time (when flight is ready to push back)
CTOT => Calculated Take Off Time (given by the European control management its the slot when the flight should depart (CTOT -5/+10 min))
TSAT => Target Start up Approval Time, when ATC give permission to aircraft to start bush back from its stand
EXOT => Estimated Taxi Out Time

What are TOBT, CTOT, TSAT?

these are ACDM terms
TOBT => Target Off Block Time (when flight is ready to push back)
CTOT => Calculated Take Off Time (given by the European control management its the slot when the flight should depart (CTOT -5/+10 min))
TSAT => Target Start Approval Time, when ATC give permission to aircraft to start bush back from its stand

And what is ACDM?

ACDM => Airport Collaborative Decision Making
its a system aims to enhance the performance inside any airport
https://www.eurocontrol.int/articles/airport-collaborative-decision-making-cdm

This will depend on a number of factors, namely aircraft wake turbulence category, aircraft speed, planned departure route, aerodrome layout, whether or not surveillance (radar) is available, weather conditions, local rules for separation of departing aircraft and probably a few more I can't think of right now.

@J.Hougaard if I have a micro service to calculate the EXOT based on aircraft type, speed, weather condition and other factors, Do you think that would help me to set a fixed minimal seperation time for one runway/airport, or to calculate the seperation based on flight exot

can you provide a sample of  wake turbulence category list?

@FarahAmawi you've just introduced another acronym (EXOT) into the fray. It would be good to [edit] your post to include a definition of each of these.

@FarahAmawi you might want to improve the question by puting explanations into the question itself instead of adding comments.